Residue-free flux, solder paste, soldering process, manufacturing method for soldered products, manufacturing method for BGA packages

Abstract

To provide: a flux which contains no reducing agent or no activator and can render solder joints residue-free; and a solder paste prepared using the flux.SOLUTION: A flux contains: a first solvent of which the temperature at which the mass becomes zero as measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min. and a temperature raising rate of 10°C / min. is 180°C or higher and lower than 260°C; a second solvent of which the temperature at which the mass becomes zero as measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min. and a temperature raising rate of 10°C / min. is 100°C or higher and lower than 220°C; and a fatty acid amide. The content of the first solvent is smaller than that of the second solvent. The flux contains no reducing agent for reducing and removing an oxide film on the surface of a solder or no activator for improving the reducibility, and a mixture of the flux with a solder powder can be used as a solder paste.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a flux, a solder paste, a soldering process, and a method for manufacturing a soldered product, and in particular to a flux that can form a residue-free solder paste, a residue-free solder paste, a soldering process using the solder paste, a method for manufacturing a soldered product, and a method for manufacturing a BGA package. [Background technology]

[0002] In the manufacture of power devices, large-area solder joints are made between semiconductor chips and DBC (Direct Bonded Copper) substrates, and between DBC substrates and base plates. Solder materials can be solder foil or solder paste, the former of which requires a fixture, and the latter of which requires cleaning of flux residue after soldering.

[0003] Solder paste typically contains solder powder and flux. Flux components include reducing agents, activators, thixotropic agents (binders), solvents, and tackifier resins. The reducing agent removes the oxide film on the surface of the solder powder and the surface of the object to be soldered during soldering, while the activator improves reduction and improves the wettability of the solder.

[0004] However, flux remains as flux residue after soldering. Among the flux components, reducing agents and activators have a significant impact on soldering performance, corrosion, and migration. A high reduction effect improves solderability. However, these active ingredients are easily ionized and have a strong affinity with water, making them susceptible to corrosion and ion migration.

[0005] Therefore, when using solder paste containing a reducing agent or activator, it is necessary to clean the flux residue after soldering. However, cleaning the flux residue increases the cost of the process. In addition, the cleaning process generates waste liquid, which places a heavy burden on the environment and requires reduction. Therefore, Patent Document 1 discloses a solder paste that is free of reducing agents and activators and does not require cleaning (paragraph 0001). When this solder paste is used, the flux residue is mainly the contained thixotropic agent, and the amount of residue is extremely small, at less than 1% by mass of the entire solder joint. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 057651 Summary of the Invention [Problem to be solved by the invention]

[0007] However, even when using the above solder paste, the total amount of flux residue increases as the solder joint area increases. Furthermore, because the area is large, the flux is difficult to volatilize, remaining inside the solder joint and causing voids. Furthermore, areas where voids occur have poor heat dissipation, leading to a decrease in the performance of power devices. In view of the above-mentioned problems, the present invention aims to provide a flux that does not contain a reducing agent or an activator and that can produce a solder joint without residue and with low voids, and a solder paste using said flux. Note that "residue-free" refers to a state in which there is no or almost no flux residue after soldering. Specifically, this refers to flux residue that cannot be detected by visual observation after soldering, or flux residue that can be detected by visual observation but is not detectable by infrared spectroscopy (IR). "Low voids" refers to voids of less than 5% when the soldered part is observed with an X-ray transmission device. Note that "%" refers to the area ratio of a two-dimensional transmission image. [Means for solving the problem]

[0008] Because fatty acid amides can evaporate along with the evaporation of certain solvents, the inventors used fatty acid amides as a thixotropic agent and two solvents that differ in the temperatures at which their mass becomes zero in thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L per minute and a heating rate of 10°C per minute. They then prepared a flux that did not contain a reducing agent or activator and contained the two solvents (first solvent, second solvent) and fatty acid amide. They discovered that solder paste using this flux can be made to leave no flux residue, and therefore no flux residue remains inside, resulting in low voids in the solder joint, and thus completed the present invention.

[0009] A flux according to a first aspect of the present invention comprises: a first solvent having a mass-zero temperature of 180°C or higher but lower than 260°C when measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a heating rate of 10°C per minute; a second solvent having a mass-zero temperature of 100°C or higher but lower than 220°C when measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a heating rate of 10°C per minute; and a fatty acid amide; the content of the first solvent is less than the content of the second solvent, and the flux does not contain a reducing agent for reducing and removing an oxide film on the solder surface or an activator for improving reducibility, and a mixture with solder powder can form a solder paste, and no flux residue can be produced. As used herein, "zero mass by thermogravimetry" refers to a value of zero or close to zero at which the TG curve ceases to fluctuate with increasing temperature (or at which no fluctuations are observed with increasing temperature). The "fatty acid amide" acts as a thixotropic agent, preventing separation of the solder powder from other components or preventing sagging, while the "solvent" allows for viscosity adjustment. The second solvent preferably evaporates at a temperature lower than the melting point of the solder powder. The first solvent preferably evaporates the fatty acid amide upon evaporation. A "reducing agent" refers to a component that removes oxide films, and an "activator" refers to a component that improves reducibility. "Containing no reducing agent" refers to a reducing agent-free product, or, if present, to an amount that does not impair the effects of the present invention. "Containing no activator" refers to a reducing agent-free product, or, if present, to an amount that does not impair the effects of the present invention. In other words, the amount is such that cleaning is not required, flux residue is eliminated, and the solder joint has low voids. Thus, other components such as a reducing agent, an activator, and additives may be included as long as they do not impair the effects of the present invention. That is, the flux of the present invention may be a flux consisting essentially of a first solvent, a second solvent, and a fatty acid amide, and the solder paste may be a solder paste consisting essentially of a solder powder, a first solvent, a second solvent, and a fatty acid amide. In this specification, the phrase "consisting of" means "essentially consisting of." By configuring in this way, it is possible to obtain a flux that leaves no flux residue and can reduce voids in the solder joint.

[0010] A flux according to a second aspect of the present invention is the flux according to the first aspect of the present invention, wherein the temperature of the first solvent is higher than the temperature of the second solvent, and the difference between the temperatures of the first solvent and the second solvent is 15°C or more. In this configuration, the combination of the first solvent and the second solvent becomes more preferable.

[0011] A flux according to a third aspect of the present invention is the flux according to the first or second aspect of the present invention, and contains 2 to 15 mass % of the first solvent, 70 to 86 mass % of the second solvent, and 6 to 24 mass % of the fatty acid amide. By configuring in this way, the ratio of the flux components can be made more appropriate.

[0012] A flux according to a fourth aspect of the present invention is the flux according to any one of the first to third aspects of the present invention, comprising the first solvent, the second solvent, and the fatty acid amide. By configuring in this way, it is possible to obtain a flux that leaves no flux residue and can reduce voids in the solder joint.

[0013] A solder paste according to a fifth aspect of the present invention contains solder powder and the flux according to any one of the first to fourth aspects of the present invention. By configuring in this manner, it is possible to obtain a solder paste that leaves no flux residue after soldering and can reduce voids in the soldered joint.

[0014] A solder paste according to a sixth aspect of the present invention comprises a solder powder and the flux according to the fourth aspect of the present invention. By configuring in this manner, it is possible to obtain a solder paste that leaves no flux residue after soldering and can reduce voids in the soldered joint.

[0015] A solder paste according to a seventh aspect of the present invention is the solder paste according to the fifth or sixth aspect of the present invention, wherein the solder powder contains powder having a particle size of 38 μm or less in a proportion of 40 mass % or less of the total amount of solder powder. With this configuration, at least 60% by mass of the solder powder has a particle size exceeding 38 μm, maintaining gaps between the solder powder particles that are more suitable for the introduction of reducing gas, making it easier for the reducing gas to penetrate. Furthermore, larger particle sizes result in larger gaps between particles, making it easier for the solvent and fatty acid amide to evaporate. In particular, for power devices with large-area bonding, it is difficult to evaporate the solvent and fatty acid amide in the center, so the above particle size is more preferable. Figure 7 shows an example of a scanning electron microscope (SEM) image of the gaps formed between the solder powder particles.

[0016] A soldering process according to an eighth aspect of the present invention comprises the steps of: providing a solder paste according to any one of the fifth to seventh aspects of the present invention; introducing a reducing gas that reduces the solder powder; and melting the solder powder. This configuration allows for zero flux residue. Furthermore, because the solder paste is free of reducing agents and activators, the volatile components of the flux are not ionic during soldering, so there is no risk of corrosion to the board or components.

[0017] A ninth aspect of the present invention provides a method for manufacturing a soldered product, comprising: an application step of applying a solder paste to an object to be soldered, the solder paste including a first solvent, a second solvent having a lower temperature than the first solvent at which the mass becomes zero when measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L per minute and a heating rate of 10°C per minute, a fatty acid amide, and a solder powder; an evaporation step of heating the object to be soldered to which the solder paste has been applied within a range that does not melt the solder powder, thereby evaporating the second solvent; a reduction step of reducing the solder powder and the object to be soldered with a reducing gas, either in parallel with or after the evaporation step; and a solder melting step of heating the solder powder and the object to be soldered after the reduction step, thereby melting the solder powder. The first solvent and the fatty acid amide evaporate together with the second solvent in the evaporation step, or evaporate as a result of heating in the solder melting step, leaving no flux residue. With this configuration, the solder powder does not melt during reduction, and the gaps created between the solder powder allow for effective reduction of the solder powder and the object to be soldered. Furthermore, this method of manufacturing soldered products has the advantages of being able to eliminate flux residue, and because the solder paste is free of reducing agents and activators, the volatile components of the flux during soldering are not ionic, preventing corrosion of the board or components.

[0018] A method for manufacturing a soldered product according to a tenth aspect of the present invention is the method for manufacturing a soldered product according to the ninth aspect of the present invention, wherein the evaporation process further comprises a decompression process for decompressing the space in which the object to be soldered is placed. This configuration can promote evaporation of the flux components that evaporate in the evaporation step.

[0019] A method for manufacturing a soldered product according to an eleventh aspect of the present invention is the method for manufacturing a soldered product according to the ninth or tenth aspect of the present invention, wherein the evaporation step involves heating the object to be soldered in a vacuum. "Vacuum" refers to a space with a pressure lower than atmospheric pressure (so-called reduced pressure). This configuration can promote evaporation of the solvent. Furthermore, even solvents whose boiling points at normal pressure are higher than the temperature during reduction can be evaporated efficiently, increasing the variety of solvents that can be used.

[0020] A method for manufacturing a soldered product according to a twelfth aspect of the present invention is a method for manufacturing a soldered product according to any one of the ninth to eleventh aspects of the present invention, in which the evaporation process creates gaps between the solder powders, and the reduction process involves introducing a reducing gas into the gaps while the solder powder and the object to be soldered are in a vacuum. This configuration allows the reducing gas to easily penetrate into gaps between the solder powder particles and the like.

[0021] A method for manufacturing a soldered product according to a thirteenth aspect of the present invention is a method for manufacturing a soldered product according to any one of the ninth to twelfth aspects of the present invention, wherein the solder melting step comprises heating the solder powder and the object to be soldered while they are in a vacuum to melt the solder powder and obtain an integrated solder joint; a vacuum breaking step after the solder melting step, in which the vacuum is broken and the internal cavity (void) of the solder joint is compressed, reduced in size, or eliminated; and a cooling step after the vacuum breaking step, in which the object to be soldered is cooled. By configuring it in this manner, voids can be crushed while the solder is molten during the vacuum breaking process, and the solder can be solidified after the voids are crushed, thereby further suppressing the reduction in fatigue life due to voids in the solder.

[0022] A method for manufacturing a soldered product according to a 14th aspect of the present invention is the method for manufacturing a soldered product according to any one of the 9th to 13th aspects of the present invention, wherein the reducing gas is formic acid gas. This solder paste is suitable for gases that are often used as reducing gases, and can reduce the solder powder and the object to be soldered at temperatures below 300°C.

[0023] A fifteenth aspect of the present invention is a method for manufacturing a BGA package using the flux according to any one of the first to fourth aspects of the present invention as a temporary fixing agent for solder balls. The method for manufacturing a BGA package includes the following steps: a coating step of coating a BGA package substrate with a flux containing a first solvent, a second solvent having a temperature at which the mass becomes zero in thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a heating rate of 10°C / min lower than that of the first solvent, and a fatty acid amide; a temporary fixing step of temporarily fixing solder balls to the applied flux; and an evaporation step of heating the BGA package substrate coated with the flux within a range that does not melt the solder balls, thereby evaporating the second solvent. The method includes: a reduction step in which, concurrently with or after the evaporation step, the solder balls and the BGA package substrate are reduced with a reducing gas; and a formation step in which, after the reduction step, the solder balls and the BGA package substrate are heated to bond the solder balls to the BGA package substrate and form solder bumps. The first solvent and the fatty acid amide evaporate together with the second solvent in the evaporation step, or evaporate as a result of heating in the formation step, and no flux residue can be left. This configuration allows the production of a BGA package with no flux residue and low voids in the solder joints.

[0024] A method for manufacturing a soldered product according to a sixteenth aspect of the present invention includes: an application step of applying a solder paste containing a first solvent, a second solvent having a temperature lower than that of the first solvent at which the mass becomes zero in thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a heating rate of 10°C / min, a fatty acid amide, and solder powder to an object to be soldered; a bump placement step of placing solder bumps of a BGA package on the applied solder paste; and a bump placement step of heating the object to be soldered to which the solder paste has been applied within a range that does not melt the solder powder and the solder bumps, thereby forming a solder paste. The method comprises: an evaporation step of evaporating the second solvent; a reduction step of reducing the solder powder, the object to be soldered, and the solder bumps with a reducing gas in parallel with or after the evaporation step; and a solder melting step of heating the solder powder, the object to be soldered, and the solder bumps after the reduction step to melt the solder powder and the solder bumps; the first solvent and the fatty acid amide evaporate together with the second solvent in the evaporation step, or evaporate as they are heated in the solder melting step, and no flux residue can remain. With this configuration, when the object to be soldered is a printed circuit board, a BGA package can be mounted, no flux residue remains, and the solder joint can have few voids. [Effects of the Invention]

[0025] According to the present invention, it is possible to obtain a flux that does not contain a reducing agent or an activator, does not require cleaning, leaves no flux residue, and has few voids in the solder joint. Furthermore, a mixture of this flux and solder powder can become a solder paste that does not require cleaning, leaves no residue, and has few voids in the solder joint. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a diagram showing an outline of a method for manufacturing a soldered product, where A is a conventional method and B is the method of the present invention. [Figure 2] 1 is a flowchart illustrating a method for manufacturing a soldered product of the present invention. [Figure 3] 1 is a schematic diagram of a soldering apparatus 1. FIG. [Figure 4] 1 is a flowchart illustrating a soldering procedure using the soldering apparatus 1. [Figure 5] 10 is a flowchart illustrating another soldering procedure using the soldering apparatus 1. [Figure 6] 1 is a graph illustrating a temperature profile during reflow. [Figure 7] 1 is a scanning electron microscope (SEM) image showing gaps formed between the solder powder particles. DETAILED DESCRIPTION OF THE INVENTION

[0027] This application is based on Patent Application No. 2018-043396 filed in Japan on March 9, 2018, the contents of which form a part of the contents of the present application. The present invention will be more fully understood from the following detailed description. Further applicability of the present invention will become apparent from the following detailed description. However, the detailed description and specific examples are preferred embodiments of the present invention and are set forth for illustrative purposes only. From this detailed description, various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art. The applicant does not intend to dedicate any of the described embodiments to the public, and modifications and alternatives that may not literally fall within the scope of the claims are considered part of the invention under the doctrine of equivalents.

[0028] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, identical or similar reference numerals are used to designate identical or corresponding parts, and redundant explanations will be omitted. Furthermore, the present invention is not limited to the following embodiments.

[0029] [Flux] A flux according to a first embodiment of the present invention will be described. The flux of the present invention contains a fatty acid amide as a thixotropic agent and two solvents, a first solvent and a second solvent, which have different temperatures at which they become zero in thermogravimetry at a temperature rise rate of 10°C per minute with a nitrogen flow rate of 0.2 to 0.3 L per minute, but does not contain a reducing agent or an activating agent, or if it does contain them, the amount is not more than the amount that does not impair the effects of the present invention. The reducing agent here is a substance that exhibits a reducing action and removes oxide films from the surface of the solder powder or the surface of the object to be soldered during soldering, such as rosin or a rosin derivative. The activator is a substance that improves the reducing property and the wettability of the solder, and is, for example, an amine hydrohalide, an organic acid, etc. Examples of the amine hydrohalide include diethylamine hydrobromide and cyclohexylamine hydrobromide, etc. Examples of the organic acid include glutaric acid, adipic acid, azelaic acid, sebacic acid, stearic acid, and benzoic acid. The flux of the present invention may contain compounds (additives, etc.) other than the fatty acid amide and the solvent, except for the reducing agent and activator, as long as the effects of the invention are obtained.

[0030] [Solder paste] A solder paste according to a second embodiment of the present invention will now be described. The solder paste of the present invention contains the above flux and solder powder. The solder paste of the present invention may contain compounds (additives, etc.) other than the flux and solder powder, except for the reducing agent and activator, as long as the effects of the present invention can be obtained.

[0031] When soldering is performed using the solder paste of the present invention, a reducing gas is used for reduction. The solder powder contained in the solder paste of the present invention is preferably one that does not melt at the reduction temperature and pressure during reduction using the reducing gas. In other words, the temperature at which the solder powder melts is any temperature higher than the reduction temperature, and in this embodiment, it is preferably a temperature 10 to 50°C higher than the reduction temperature.

[0032] [solvent] The second solvent is preferably one that evaporates (vaporizes) at or below the reduction temperature. The minimum temperature at which the evaporation of the second solvent is completed regardless of the atmospheric pressure (hereinafter referred to as the evaporation temperature) is any temperature that is lower than or equal to the reduction temperature. Even if the boiling point of a solvent at normal pressure is higher than the reduction temperature, it is possible to use the solvent as the second solvent by lowering the evaporation temperature below the reduction temperature using a mechanism for adjusting the atmospheric pressure. In this way, the second solvent may be any solvent that evaporates at or below the reduction temperature at a predetermined atmospheric pressure. That is, the flux and solder paste of the present invention contain materials that have the following relationship at a given atmospheric pressure: · Evaporation temperature of the second solvent ≦ Reduction temperature < Melting point of the solder powder The "melting point" mentioned above refers to the temperature at which a substance melts regardless of atmospheric pressure. In this way, when reduction is performed using a reducing gas, the solder powder may be solid and the second solvent may be gaseous, and the solder powder and second solvent are appropriately combined according to the temperature during reduction.

[0033] The first solvent may begin to evaporate at a temperature lower than its original boiling point as the second solvent evaporates, and may evaporate (vaporize) together with the second solvent during the evaporation process, or, unlike the second solvent, may evaporate as the temperature rises from the reduction temperature. Thus, the timing at which the first solvent disappears due to evaporation may vary depending on the type of first solvent. Note that, since the fatty acid amide must be evaporated as the first solvent evaporates, it is preferable that the first solvent be a solvent that can evaporate the fatty acid amide during evaporation.

[0034] The first solvent is preferably one whose mass becomes zero at a temperature of 180°C or higher but lower than 260°C when measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a temperature increase rate of 10°C / min. The second solvent is preferably one whose mass becomes zero at a temperature of 100°C or higher but lower than 220°C when measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a temperature increase rate of 10°C / min. Thermogravimetry (TG) was performed using a thermal analyzer (TG-DTA) TG8120 manufactured by Rigaku Corporation, with approximately 5 mg (approximately 5 mg) placed in an aluminum pan. The difference between the temperature of the first solvent and the temperature of the second solvent is preferably at least 15°C, more preferably 25°C or more, and particularly preferably 35°C or more.

[0035] Examples of the first solvent include tetraethylene glycol dimethyl ether, diethylene glycol monophenyl ether, 1-hexadecanol, 2-hexyldecanol, 1-octadecanol, isoarachyl alcohol, isooctadecanol, trimethylolpropane, triethylene glycol, tetraethylene glycol, 1,8-octanediol, 2,4-diethyl-1,5-pentanediol, etc. The solvents can be used alone or in combination.

[0036] Examples of the second solvent include glycol-based, glycol ether-based, and alcohol-based solvents. Specific examples include triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monobutyl acetate, dipropylene glycol, diethylene glycol-2-ethylhexyl ether, α-terpineol, menthol, benzyl alcohol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,5-dimethyl-2,5-hexanediol, 2-methylpentane-2,4-diol, 2,2-dimethyl-1,3-propanediol, butyl benzoate, diethyl adipate, dodecane, tetradecene, ethylene glycol, diethylene glycol, hexylene glycol, 1,5-dihydroxypentane, and oleyl alcohol. The solvents can be used alone or in combination.

[0037] [Thixotropic agent] Thixotropic agents adjust the viscosity of the solder paste and promote adhesion of materials. Fatty acid amides are used as thixotropic agents. Examples of fatty acid amides include amide-based thixotropic agents. The amide-based thixotropic agents are compounds containing an amide bond (-CONH-), and include, for example, higher fatty acid amides such as stearic acid amide, palmitic acid amide, lauric acid amide, behenic acid amide, and 12-hydroxystearic acid amide, unsaturated fatty acid monoamides such as ricinoleic acid amide, erucic acid amide, and oleic acid amide, substituted amides such as N-lauryl lauric acid amide and N-stearyl stearic acid amide, and methylol stearic acid amide. Examples of the thixotropic agent include ethylene oxide adducts of fatty acid amides, fatty acid ester amides, fatty acid ethanol amides, substituted ureas such as N-butyl-N'-stearyl urea, saturated fatty acid bisamides such as methylene bisstearic acid amide, ethylene bislauric acid amide, ethylene bishydroxystearic acid amide, unsaturated fatty acid bisamides such as methylene bisoleic acid amide, and aromatic bisamides such as m-xylylene bisstearic acid amide. These amide-based thixotropic agents can be used alone or in combination. The shape is not particularly limited, and may be granular or flake-like. Furthermore, a thixotropic agent swollen with a solvent may also be used. Among the thixotropic agents, it is more preferable to use higher fatty acid amides, etc., since they tend to volatilize easily together with the first solvent. Particularly preferred are higher fatty acid amides and unsaturated fatty acid amides with a melting point of 80°C or higher and 110°C or lower at normal pressure.

[0038] These thixotropic agents increase the viscosity of the flux and solder paste, increase the thixotropic ratio of the solder paste (improving printability), improve heat sagging, and prevent the separation of solder powder and flux. These thixotropic agents evaporate when the first solvent evaporates, so very little remains in the solder joint. Even if they volatilize and re-adhere to the board or components, they are not active substances and will not cause corrosion.

[0039] [Solder powder] The alloy composition of the solder powder is not particularly limited. Various solder alloys currently used for bump formation and printed circuit board mounting can be used. Examples include powders of lead-free solder alloys such as Sn-Ag solder, Sn-Ag-Cu solder, Sn-Ag-Cu-Bi solder, Sn-Ag-In-Bi solder, Sn-Cu solder, Sn-Zn solder, and Sn-Bi solder, which are used as lead-free solders, as well as the variable melting point alloy A-FAP.

[0040] The average particle size of the solder powder can be, for example, in the range of 15 to 53 μm or 20 to 53 μm. However, depending on the size of the printing aperture, the diameter may be changed to a larger or smaller size as appropriate. Considering the introduction of reducing gas into the gaps between the solder powder particles to further improve reduction, it is more preferable that the solder powder contains powder particles with a particle size of 38 μm or less at a ratio of 40 mass% or less of the total amount of solder powder. Even more preferable is 30 mass% or less, and particularly preferable is 20 mass% or less. Figure 7 shows an example of a scanning electron microscope (SEM) image of the gaps between solder powder particles that occur due to differences in particle size. In this specification, the term "average particle size" refers to the particle size at an integrated value of 50% in the particle size distribution determined by a laser diffraction / scattering method.

[0041] [Reducing gas] Examples of reducing gases used with the solder paste include hydrogen, carboxylic acid gases such as formic acid, organic acid gases other than carboxylic acids, organic compound gases other than organic acids, and other reducing gases other than organic compounds. Regardless of whether atmospheric pressure or vacuum is used, the temperature during reduction is preferably 150 to 450°C. For example, when the reducing gas is formic acid, the temperature during reduction is 150 to 300°C, preferably 160 to 250°C, and particularly preferably 170 to 230°C. When the reducing gas is hydrogen, the temperature is 250 to 450°C, preferably 260 to 400°C, and particularly preferably 270 to 350°C. For example, when formic acid is used as the reducing gas and the reduction temperature is set to about 200° C., the second solvent is preferably one that evaporates at about 200° C. or less. Formic acid is preferable because it can be reduced at a lower temperature than other reducing gases.

[0042] [composition] The composition of the flux of the present invention is 6 to 24 mass% fatty acid amide, 2 to 15 mass% first solvent, and 70 to 86 mass% second solvent, preferably 9 to 15 mass% fatty acid amide, 4 to 12 mass% first solvent, and 76 to 84 mass% second solvent. For example, the first solvent is 4 mass% fatty acid amide, 12 mass% first solvent, and 84 mass% second solvent. The composition of the solder paste of the present invention is 80 to 99 mass % solder powder and 1 to 20 mass % of the flux, and preferably 85 to 95 mass % solder powder and 5 to 15 mass % of the flux.

[0043] The flux of the present invention is typically a mixture of a fatty acid amide, a first solvent, and a second solvent in the above-mentioned ratio. The solder paste of the present invention is typically a mixture of a solder powder, a fatty acid amide, a first solvent, and a second solvent in the above-mentioned ratio to form a paste. The amounts of the fatty acid amide and the solvent can be changed as needed depending on the degree of viscosity adjustment. The fatty acid amide and the solvent can be mixed by stirring while heating. The mixture with the solder powder can be mixed at room temperature using a stirrer.

[0044] [Manufacturing method for soldered products] With reference to Figure 1, an outline of a method for manufacturing a soldered product according to a third embodiment of the present invention will be explained, comparing it with a conventional method. Method A in Figure 1 is the conventional method, in which the solder paste used contains solder powder and, as flux, a reducing agent, an activator, a thixotropic agent, and a solvent. Method B is a method for manufacturing a soldered product according to the present invention, in which the solder paste used contains solder powder and, as flux, a thixotropic agent (fatty acid amide), a first solvent, and a second solvent, but does not contain a reducing agent or an activator.

[0045] In the following description, an object to be soldered T and a solder paste S are used as the members to be joined in FIG. First, in Method A, solder paste S' is applied to the workpiece T by screen printing or other methods (A1). When the workpiece T and solder paste S' are heated as shown in Figure 1, the solvent begins to evaporate (A2). The workpiece is further heated, and reduced by a molten flux containing a reducing agent and an activator (A3). The workpiece is then heated further to above the solder melting temperature, and soldering is performed (A4). Approximately 10% by mass of the flux in the solder paste remains as flux residue, which is removed by washing (A5).

[0046] In Method B, solder paste S is applied to the workpiece T by screen printing or other methods (B1). When the workpiece T and solder paste S shown in Figure 1 are heated, the evaporation of the second solvent begins (B2). The workpiece is further heated to the reduction temperature, and reduction is performed with reducing gas F (B3). During reduction (B3), the fatty acid amide (thixotropic agent) and the first solvent may remain, depending on various conditions, such as the type of first solvent and the time until reduction begins. The workpiece is further heated above the solder melting temperature, and soldering is performed (B4). If the first solvent remains, it evaporates by the time soldering is completed, and the fatty acid amide (thixotropic agent) evaporates along with it. Therefore, almost no flux residue remains, and cleaning is naturally unnecessary. In Method B, the melting temperature of the solder powder is higher than the reduction temperature, so the solder powder does not melt during reduction. This creates gaps between the solder powder, facilitating the penetration of the reducing gas and reduction. The reduction may be carried out simultaneously with or after the evaporation of the second solvent.

[0047] The method for manufacturing a soldered product according to the third embodiment of the present invention will be described in more detail with reference to Fig. 2. Fig. 2 is a flow chart showing the method for manufacturing a soldered product. 2 and 3, the following description will be given using a substrate W, solder paste S, and electronic component P as the members to be joined, as shown in FIG. (1) Solder paste supply process The solder paste providing step is a step of preparing the solder paste according to the second embodiment of the present invention for use, and may be the manufacturing of solder paste or the preparation of an already manufactured solder paste.

[0048] (2) Solder paste application process The solder paste is applied to the object to be soldered using a solder paste printer (or screen printer) or the like. Typically, a mask (mold) called a metal mask, for example, a metal plate with holes drilled into it about 30 to 300 μm thick, is used, and printing is performed using the squeegee of the printer. A manual device in which the squeegee is operated by hand can also be used. Alternatively, application can be performed using a syringe.

[0049] (3) Evaporation of the second solvent, reduction of the joined components, and solder melting The second solvent evaporation step, the bonded member reduction step, and the solder melting step will be described in more detail using the soldering apparatus 1 shown in FIG. The objects to be soldered, on which the solder paste S is applied, are a substrate W and an electronic component P. Formic acid gas is used as the reducing gas. In the following explanation, the method for manufacturing a soldered product according to the third embodiment of the present invention will be explained together with the operation of the soldering apparatus 1 of FIG. 3, but it may also be performed by other apparatus.

[0050] First, the soldering apparatus 1 will be described with reference to Fig. 3. Fig. 3 is a schematic diagram of the soldering apparatus 1. The soldering apparatus 1 includes a processing section 10 having a chamber 11 that forms a processing space 11s where solder joining of members to be joined is performed, a formic acid supply section 20 serving as a reducing gas supply section that supplies formic acid gas F as a reducing gas to the chamber 11, a catalyst unit 33 serving as a reducing gas processing section that reduces the concentration of formic acid gas F within the soldering apparatus 1 before it is discharged, a control device 50 that controls the operation of the soldering apparatus 1, and a housing 100 that houses these components.

[0051] The soldering apparatus 1 is an apparatus that joins a substrate W and an electronic component P with solder paste S. Both the substrate W and the electronic component P have metal portions on their surfaces, and are joined so that the metal portions are conductive via solder. The substrate W and the electronic component P are carried into a chamber 11 with the solder paste S sandwiched between them, and the solder melts and joins them inside the chamber 11. Hereinafter, the substrate W, solder paste S, and electronic component P stacked together in a state where the solder is not melted will be referred to as a member to be joined B, and the state in which the solder has melted and the substrate W and electronic component P are joined, i.e., the joined member, will be referred to as a soldered product C.

[0052] The chamber 11 is configured so that the processing space 11s can be sealed by closing the loading / unloading port 11a with the shutter 11d. The chamber 11 is made of a material and has a shape that can withstand a reduction in the processing space 11s to approximately 10 Pa (absolute pressure). Inside the chamber 11, a carrier plate 12 on which the workpiece B is placed and a heater 13 for heating the carrier plate 12 are provided.

[0053] The heater 13 is configured to be able to heat the carrier plate 12 to a bonding temperature that is higher than the melting temperature of the solder.

[0054] The formic acid supply unit 20 introduces formic acid gas F into the chamber 11. In this description, formic acid gas F is used as the reducing gas, but any other reducing gas may be used, such as a carboxylic acid gas other than formic acid gas F, an organic acid gas other than a carboxylic acid, an organic compound gas other than an organic acid, or another reducing gas other than an organic compound, as long as it can reduce the metal oxide generated on the bonding surfaces of the substrate W and the electronic component P. Examples of other reducing gases include hydrogen gas. In this description, formic acid gas F is used as the reducing gas from the viewpoint of lowering the reduction temperature below the melting temperature of the solder and from the viewpoint of ease of availability.

[0055] The catalyst unit 33 is a device that reduces the concentration of formic acid in the exhaust gas E discharged from the soldering apparatus 1 to a concentration that does not affect the environment. Note that the gas G is a general term for the gas discharged from the chamber 11.

[0056] The vacuum pump 31 is disposed as a decompression pump that exhausts the gas G from the chamber 11 so that the pressure in the chamber 11 can be reduced to approximately 10 Pa (absolute pressure).

[0057] The control device 50 is configured to be able to open and close the shutter 11d. The control device 50 is also configured to be able to heat the carrier plate 12 by turning the heater 13 on and off and changing its output. The control device 50 is also configured to be able to supply formic acid gas F to the chamber 11. The control device 50 is also configured to be able to control the start and stop of the vacuum pump 31. The control device 50 also stores the operation sequence of the soldering device 1, which will be described later.

[0058] Continuing with reference to Fig. 4, a method for manufacturing a soldered product C according to an embodiment of the present invention will be described. Fig. 4 is a flowchart showing the soldering procedure for the soldered product C. When referring to the configuration of the soldering apparatus 1 in the following description, Fig. 3 will be referenced as appropriate.

[0059] When a button (not shown) for opening shutter 11d is pressed to load workpiece B into soldering apparatus 1, control device 50 activates vacuum pump 31 to begin evacuating gas G from chamber 11 (S1), and then opens shutter 11d. At the same time, control device 50 moves carrier plate 12 so that most of carrier plate 12 is outside chamber 11. By discharging gas G from chamber 11 before opening shutter 11d, gas G from chamber 11 can be prevented from flowing out of soldering apparatus 1 through inlet / outlet 11a even when shutter 11d is opened. Once shutter 11d is opened, most of carrier plate 12 is outside chamber 11, and workpiece B is placed on carrier plate 12, workpiece B is loaded into chamber 11 as carrier plate 12 moves into chamber 11 (S2).

[0060] Once the workpieces B have been loaded into the chamber 11, the control device 50 closes the shutter 11d to seal the chamber 11. Next, to remove the air that flowed into the chamber 11 when the shutter 11d was open and to create an inert gas atmosphere, the control device 50 evacuates the gas G from the chamber 11 and then introduces the inert gas N. By repeating this process, the oxygen concentration in the chamber 11 is reduced (S3). The oxygen concentration is preferably 5 ppm or less. The inert gas N is, for example, nitrogen gas.

[0061] Next, the control device 50 turns on the heater 13 to raise the temperature of the carrier plate 12, and therefore the temperature of the workpieces B, to a temperature at which the second solvent contained in the solder paste S evaporates (evaporates) (S4). As the temperature rises, mainly the second solvent evaporates and is removed from the solder paste S. In this embodiment, the pressure inside the chamber 11 can be made vacuum (reduced pressure) to promote evaporation of the second solvent. In this way, before supplying the formic acid gas F, heating can be performed in an atmosphere that does not contain formic acid gas F to evaporate the second solvent and form gaps between the solder powder particles. In this embodiment, the vaporization temperature is lower than the reduction temperature, but the vaporization temperature may be the same as the reduction temperature described below. If they are the same, evaporation of part of the second solvent and reduction of the bonded member B occur simultaneously. In other words, there are cases where step (S4) and the subsequent steps (S5) and (S6) are performed in parallel.

[0062] After the second solvent evaporates and gaps are formed between the solder powder particles, the control device 50 then supplies formic acid gas F from the formic acid supply unit 20 into the chamber 11 (S5) and keeps the heater 13 ON to raise the temperature of the carrier plate 12, and therefore the temperature of the workpieces B, to a reduction temperature (S6). The reduction temperature is the temperature at which the oxides in the workpieces B are reduced by formic acid. In this embodiment, the reduction temperature is lower than the melting temperature of the solder powder contained in the solder paste S. Therefore, the formic acid gas easily penetrates into the gaps formed by the unmelted solder powder, thereby effectively removing the oxide film before the workpieces B are solder-bonded. The supply of formic acid gas F is performed after creating a vacuum in the chamber 11, which makes it easier for the formic acid gas F to penetrate into the gaps between the solder powder particles. The process of supplying formic acid gas F into the chamber 11 (S5) and the process of raising the temperature of the workpieces B to a reduction temperature (S6) correspond to the reduction process. The formic acid gas F may be supplied after the temperature has been raised to the reduction temperature.

[0063] After the reduction steps (S5, S6) are completed, the formic acid gas F atmosphere in the chamber 11 is maintained, and the output of the heater 13 is increased to raise the temperature of the carrier plate 12, and therefore the temperature of the members to be joined B, to the joining temperature, melting the solder powder and solder-joining the members to be joined B (S7). The joining temperature is any temperature higher than the melting temperature of the solder powder contained in the solder paste S, and in this embodiment, it is set to a temperature 30 to 50°C higher than the melting temperature. Note that if any first solvent remains, it evaporates between the reduction steps (S5, S6) and the joining step (S7), and as the first solvent evaporates, the fatty acid amide also evaporates and disappears.

[0064] Once the solder on the workpiece B has melted, the control device 50 turns off the heater 13. This cooling process reduces the temperature of the workpiece B. When the temperature drops below its melting point, the solder solidifies, forming a soldered product C. At this point, the carrier plate 12 may be forcibly cooled to hasten the solidification of the solder. Next, the vacuum pump 31 is activated and the main exhaust valve 41v is opened to exhaust formic acid gas F from the chamber 11 (S8). Then, an inert gas N is introduced to restore atmospheric pressure to the chamber 11. The formic acid gas F exhausted from the chamber 11 flows into the catalyst unit 33. The formic acid in the formic acid gas F is decomposed in the catalyst unit 33, reducing the formic acid concentration below a predetermined level. The gas is then exhausted from the soldering apparatus 1 as exhaust gas E (S9). Once the soldered product C is produced, the control device 50 exhausts gas G from the chamber 11 via the bypass exhaust pipe 42 (S10) and opens the shutter 11d. This allows the soldering product C to be removed from the chamber 11 (S11).

[0065] Once the soldering product C is removed from the chamber 11, the control device 50 determines whether or not continuous operation is to be performed (S12). If continuous operation is to be performed, the process returns to the step (S1) of exhausting the gas G from the chamber 11. On the other hand, if continuous operation is not to be performed, a maintenance operation is performed (S13).

[0066] In the above explanation, the temperature of the workpieces B is raised in an atmosphere of formic acid gas F to melt the solder powder in the solder paste S. However, the temperature may also be raised in a vacuum (for example, about 100 Pa (absolute pressure)) to melt the solder powder. When the temperature of the workpieces B is raised in a vacuum, the treatment and discharge steps (S8, S9) are performed immediately after the reduction steps (S5, S6). When opening the shutter 11d to remove the soldered product C from the chamber 11 (S11), if there is almost no formic acid gas F in the chamber 11, the shutter 11d may be opened without creating a negative pressure in the chamber 11 (without operating the vacuum pump 31). The solder paste used in the present invention can be free of flux residue, so solder (or flux) spatter can be suppressed even when the workpieces B are joined in a vacuum.

[0067] As an example of joining workpieces B in a vacuum, a method for manufacturing a soldered product C according to another embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the procedure for soldering the soldered product C. When referring to the configuration of the soldering apparatus 1 in the following description, Fig. 3 will be referenced as appropriate.

[0068] (S1) to (S6) are the same as the manufacturing method shown in FIG. After step S6 is completed, the control device 50 activates the vacuum pump 31 and opens the main exhaust valve 41v to exhaust the formic acid gas F from the chamber 11 and reduce the pressure inside the chamber 11 (S7). While maintaining the reduced pressure (vacuum) inside the chamber 11, the output of the heater 13 is increased to raise the temperature of the carrier plate 12, and therefore the temperature of the workpiece B, to the joining temperature (S8), melting the solder and soldering the workpiece B. After soldering the workpiece B, the control device 50 introduces inert gas N (S9) to break the vacuum inside the chamber 11. The control device 50 turns off the heater 13 and starts cooling (S10). This lowers the temperature of the workpiece B, and when it falls below its melting point, the solder solidifies, forming a soldered product C. After the soldered product C is produced, the control device 50 exhausts the gas G inside the chamber 11 via the bypass exhaust pipe 42 and opens the shutter 11d. This allows the soldering product C to be removed from the chamber 11 (S11). (S12) to (S13) are the same as the manufacturing method shown in FIG. In this way, when inert gas N is introduced into the molten solder, the voids can be compressed and crushed. If the solder is solidified after crushing the voids, the reduction in fatigue life due to the voids in the solder can be further suppressed.

[0069] As described above, according to the soldering apparatus 1, the processing section 10, the formic acid supply section 20, the catalyst unit 33, the control device 50, and other devices required for performing solder bonding in a vacuum are housed in the housing 100, so that solder bonding using formic acid gas F can be properly completed within the soldering apparatus 1. Furthermore, according to the method for producing the soldered product C of this embodiment, proper vacuum soldering can be performed using the solder paste S and formic acid gas F.

[0070] In the above explanation, the members to be joined are a substrate W and an electronic component P together with solder paste S, but the members to be joined may be members other than the substrate W and the electronic component P as long as they have a metal portion on their surface that is suitable for solder joining.

[0071] The method for manufacturing a soldered product of the present application may further include a coating step of coating the soldered object after the solder joint has been completed. The solder joint according to the present invention leaves almost no residue, so there is no problem with adhesion with the coating agent. Therefore, the solder joint is adequately protected by coating in the coating step.

[0072] The method for manufacturing a soldered product of the present application can also be used for manufacturing a BGA (Ball Grid Array) package. That is, the flux of the present application may be applied (printed) onto a BGA package substrate as a temporary fixing agent, solder balls with a particle size of about 100 to 350 μm may be placed on the flux, and the solder balls may be bonded (bumps may be formed) using the method for manufacturing a soldered product of the present application.

[0073] The method for manufacturing a soldered product of the present application can also be used for mounting a BGA package. That is, the solder paste of the present application may be applied (printed) onto a printed circuit board as a temporary fixing agent, the solder bumps of the BGA package may be placed on the solder paste, and the solder bumps may be joined using the method for manufacturing a soldered product of the present application.

[0074] As described above, the flux and solder paste of the present invention have a simpler composition, and the reduction of metal oxides, improvement of reducibility, and improvement of melting properties, which were previously performed by conventional reducing agents and activators, can be achieved by introducing a reducing gas and creating a vacuum on the equipment side. Furthermore, this composition makes it possible to produce solder joints that are residue-free and have few voids. Note that while the present invention has been described in terms of soldering, it is not limited to "soldering," and is also useful for "brazing." [Example]

[0075] Next, examples of the present invention will be described together with comparative examples. However, the present invention should not be construed as being limited to the following examples.

[0076] [material] Solder powder Solder powder (A): Sn-3Ag-0.5Cu (abbreviated as SAC305), melting point approximately 220°C, average particle size 40 μm, proportion of particles 38 μm or less 15% Solder powder (B): Sn-3Ag-0.5Cu (abbreviated as SAC305), melting point approximately 220°C, average particle size 33 μm, proportion of particles 38 μm or less 80% Solder powder (C): Sn-3Ag-0.5Cu (abbreviated as SAC305), melting point approximately 220°C, average particle size 30μm, 90% below 38μm, 5% below 20μm Solder powder (D): Sn-3Ag-0.5Cu (abbreviated as SAC305), melting point approximately 220°C, average particle size 19 μm, 90% below 25 μm, 5% below 10 μm Amide Fatty acid amide (A): Stearic acid amide (Kao Corporation) Fatty acid amide (B): Lauryl amide (manufactured by Nippon Kasei Co., Ltd.) Polyamide: Lightamide WH-255 (Kyoeisha Chemical Co., Ltd.) ·solvent First solvent (A): Trimethylolpropane (manufactured by Mitsubishi Gas Chemical Company, Inc.) First solvent (B): Isooctadecanol (Nissan Chemical Industries, Ltd.) First solvent (C): 1-hexadecanol (Tokyo Chemical Industry Co., Ltd.) First solvent (D): 2,4-dimethyl-1,5-pentanediol (Tokyo Chemical Industry Co., Ltd.) Second solvent (A): 2,2-dimethyl-1,3-hexanediol (KH Neochem) Second solvent (B): 2-methyl-1,3-hexanediol (Tokyo Chemical Industry Co., Ltd.) Second solvent (C): 3-methyl-1,5-pentanediol (Tokyo Chemical Industry Co., Ltd.) Second solvent (D): 3-methyl-1,3-butanediol (Tokyo Chemical Industry Co., Ltd.)

[0077] [Preparing solder paste 1] [Example 1] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 2 mass % of the first solvent (A), and 86 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 2] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 4 mass % of the first solvent (A), and 84 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 3] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 4 mass % of the first solvent (B), and 84 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 4] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 12 mass % of the first solvent (B), and 76 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 5] A flux was prepared by mixing 3 mass % of fatty acid amide (A), 3 mass % of fatty acid amide (B), 12 mass % of the first solvent (B), and 82 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 6] A flux was prepared by mixing 12 mass % of fatty acid amide (A), 12 mass % of fatty acid amide (B), 6 mass % of the first solvent (B), and 70 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of lead-free solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 7] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 4 mass % of the first solvent (C), and 84 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of lead-free solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 8] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 4 mass % of the first solvent (D), and 84 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of lead-free solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Comparative Example 1] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), and 88 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). Comparative Example 2 A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 21 mass % of the first solvent (B), and 67 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). Comparative Example 3 A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 21 mass % of the first solvent (A), and 67 mass % of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (A) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). Comparative Example 4 A flux was prepared by mixing 5% by mass of polyamide and 95% by mass of the second solvent (A). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of lead-free solder alloy powder (B) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)).

[0078] [Test piece preparation 1] A nickel-plated copper substrate (70 × 70 mm, 1 mm thick) was prepared as a test piece, and the solder paste of the Examples and Comparative Examples was applied to one side of the substrate in a size of 40 × 35 mm and a thickness of 600 μm (metal mask thickness). Another nickel-plated copper substrate (40 × 35 mm, 1 mm thick) was mounted on top of the applied solder paste.

[0079] [Reflow condition 1] The reflow conditions are as shown in the "Temperature Profile" in Figure 6. Preheating 1 (second solvent evaporation step): Nitrogen atmosphere (atmospheric pressure) 200°C or less Preheating 2 (second solvent evaporation step): vacuum atmosphere (200 Pa or less), 200°C, 120 seconds Preheating 3 (reduction step): Formic acid + nitrogen atmosphere (atmospheric pressure, formic acid concentration 3% Vol), 200°C, 240 seconds Main heating (solder melting process): Vacuum atmosphere (200 Pa), peak temperature 260°C, 220°C or higher, heating time 90 seconds

[0080] [Void Judgment 1] The boards on which the solder paste was printed were heated under the reflow conditions described above, and then the presence or absence of voids was checked. The checking method was to observe the solder area of ​​each board with an X-ray transmission device (Cheetah Evo manufactured by YXLON International), and those with voids of less than 5% were rated as OK, and those with voids of 5% or more were rated as NG. [Residue amount judgment 1] The flux residue after heating under the above reflow conditions was judged as NG if it was clearly visible by visual observation over a distance of 3 mm from the edge of the solder joint, or if it was clearly visible away from the solder joint, or if it could be detected by the IR method (infrared spectroscopy, PerkinElmer FT-IR Frontier, Spotlight 400). If no flux residue was visible by visual observation, or if only a small amount was visible within 3 mm from the edge of the solder joint, and it could not be detected by the IR method (infrared spectroscopy), it was judged as OK.

[0081] [Table 1] The vaporization temperature is the temperature at which the mass becomes zero in thermogravimetric measurement at a nitrogen flow rate of 0.2 to 0.3 L per minute and a temperature increase rate of 10°C per minute.

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] In Examples 1 to 8, it was possible to reduce voids and residues (no residues). Reducing voids to less than 5% is particularly effective in the manufacture of power devices in which large-area soldering is performed (such as soldering heat sinks). As mentioned above, it is preferable that the vaporization temperature of the fatty acid amide is 350°C or less. In Comparative Example 1, since the first solvent was not included, the fatty acid amide could not be evaporated, resulting in the generation of voids. In Comparative Examples 2 and 3, the amount of the first solvent was too large, so the first solvent remained as residue. In Comparative Example 4, since polyamide was used instead of fatty acid amide, flux residues remained and gas continued to be released during vaporization, resulting in many voids.

[0086] [Preparing solder paste 2] [Example 9] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 8 mass % of the first solvent (A), and 80 mass % of the second solvent (B). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (C) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 10] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 8 mass % of the first solvent (A), and 80 mass % of the second solvent (C). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (C) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 11] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 8 mass % of the first solvent (B), and 80 mass % of the second solvent (D). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (C) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). [Example 12] A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), 8 mass % of the first solvent (B), and 80 mass % of the second solvent (D). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (D) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). Comparative Example 5 A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), and 88 mass % of second solvent (D). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (C) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)). Comparative Example 6 A flux was prepared by mixing 6 mass % of fatty acid amide (A), 6 mass % of fatty acid amide (B), and 88 mass % of second solvent (B). A solder paste was prepared by mixing and stirring 8.5 mass % of the prepared flux and 91.5 mass % of solder alloy powder (C) (Sn:Ag:Cu=96.5:3.0:0.5 (mass %)).

[0087] [Test piece preparation 2] An oxygen-free copper substrate (44 × 35 mm, 1 mm thick) was prepared as a test piece, and the solder paste of the Examples and Comparative Examples was applied to one side of the substrate in a size of 12.8 × 9.8 mm and a thickness of 200 μm (metal mask thickness). A nickel-plated copper substrate (12.8 × 9.8 mm, 1 mm thick) was mounted on the applied solder paste.

[0088] [Reflow condition 2] The reflow conditions are as shown in the "Temperature Profile" in Figure 6. Preheating 1 (second solvent evaporation step): Nitrogen atmosphere (atmospheric pressure), 200°C or less, 60 seconds Preheating 2 (second solvent evaporation step): vacuum atmosphere (200 Pa or less), 200°C, 60 seconds Preheating 3 (reduction step): Formic acid + nitrogen atmosphere (atmospheric pressure, formic acid concentration 3% Vol), 200°C, 120 seconds Main heating (solder melting process): Vacuum atmosphere (200 Pa), peak temperature 250°C, 220°C or higher, heating for 40 seconds

[0089] [Void Judgment 2] The boards on which the solder paste was printed were heated under the reflow conditions described above, and then the presence or absence of voids was checked. The checking method was to observe the solder area of ​​each board with an X-ray transmission device (Cheetah Evo manufactured by YXLON International), and those with voids of less than 3% were rated as OK, and those with voids of 3% or more were rated as NG. [Residue amount judgment 2] The flux residue after heating under the above reflow conditions was judged as NG if it was clearly visible by visual observation over a distance of 3 mm from the edge of the solder joint, or if it was clearly visible away from the solder joint, or if it could be detected by the IR method (infrared spectroscopy, PerkinElmer FT-IR Frontier, Spotlight 400). If no flux residue was visible by visual observation, or if only a small amount was visible within 3 mm from the edge of the solder joint, and it could not be detected by the IR method (infrared spectroscopy), it was judged as OK.

[0090] [Table 5] The vaporization temperature is the temperature at which the mass becomes zero in thermogravimetric measurement at a nitrogen flow rate of 0.2 to 0.3 L per minute and a temperature increase rate of 10°C per minute.

[0091] [Table 6]

[0092] In Examples 9 to 12, voids and residues were reduced (residue-free). Reducing voids to less than 3% is particularly effective for soldering semiconductor chips, which require stricter standards. In Comparative Examples 5 and 6, since the first solvent was not included, the fatty acid amide could not be evaporated, resulting in the generation of voids.

[0093] All references cited in this specification, including publications, patent applications, and patents, are herein incorporated by reference to the same extent as if each reference was individually and specifically indicated to be incorporated by reference, and the contents of each reference were set forth in their entirety herein.

[0094] The use of nouns and similar referents in connection with the description of the present invention (particularly in connection with the claims that follow) shall be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The words "comprises," "has," "includes," and "comprises" shall be construed as open-ended terms (i.e., meaning "including, but not limited to"), unless otherwise noted. The recitation of numerical ranges herein is merely intended to serve as a shorthand method for individually referring to each value falling within the range, unless otherwise indicated herein, and each value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. Any examples or exemplary language used herein (e.g., "etc.") are intended merely to better illustrate the invention and do not pose a limitation on the scope of the invention, unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0095] Preferred embodiments of the invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of these preferred embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventor contemplates that skilled artisans will apply such variations as appropriate, and intends to practice the invention otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, this invention includes any combination of the above-described elements in all variations thereof unless otherwise indicated herein or otherwise clearly contradicted by context. [Explanation of symbols]

[0096] 1 Soldering equipment 11 Chamber 11s processing space 20 Formic acid supply unit 31 Vacuum pump 33 Catalytic Unit 41v main exhaust valve 42 Bypass exhaust pipe 50 Control device 100 cabinets C. Soldering products B Part to be joined F reducing gas, formic acid gas G Gas M-type, metal mask N inert gas P Electronic parts Q Squeegee S'S solder paste T Soldering object W substrate

Claims

1. a first solvent having a temperature of 180°C or higher but lower than 260°C at which a mass of 5 mg becomes zero when measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a temperature increase rate of 10°C / min; a second solvent having a temperature of 100°C or higher but lower than 220°C at which a mass of 5 mg becomes zero when measured by thermogravimetry at a nitrogen flow rate of 0.2 to 0.3 L / min and a temperature increase rate of 10°C / min; a fatty acid amide; The content of the first solvent is at least 2% by mass, The content of the second solvent is at least 70% by mass, the temperature of the first solvent is higher than the temperature of the second solvent, and the difference between the temperature of the first solvent and the temperature of the second solvent is 15°C or more; It does not contain a reducing agent for reducing and removing the surface oxide film of the solder, nor an activator for improving the reducing property. No flux residue is left behind. No residue flux.

2. The composition contains 6 to 24% by mass of the fatty acid amide, 2 to 15% by mass of the first solvent, and 70 to 86% by mass of the second solvent. The residue-free flux according to claim 1.

3. solder powder; The residue-free flux according to claim 1 or claim 2; Solder paste.

4. solder powder; The residue-free flux according to claim 1 or 2; Solder paste.

5. The solder powder contains powder having a particle size of 38 μm or less in a proportion of 40 mass % or less of the total amount of the solder powder. The solder paste according to claim 3 or 4.

6. providing a solder paste according to any one of claims 3 to 5; introducing a reducing gas to reduce the solder powder; and melting the solder powder. Soldering process.

7. an application step of applying the solder paste according to any one of claims 3 to 5 to an object to be soldered; an evaporation step of heating the object to be soldered onto which the solder paste has been applied within a range that does not melt the solder powder, thereby evaporating the second solvent; a reduction step of reducing the solder powder and the object to be soldered with a reducing gas in parallel with or after the evaporation step; a solder melting step of heating the solder powder and the object to be soldered after the reducing step to melt the solder powder; The first solvent and the fatty acid amide evaporate together with the second solvent in the evaporation step, or evaporate due to heating in the solder melting step. Manufacturing method for soldered products.

8. The evaporation step further includes a decompression step of decompressing a space in which the object to be soldered is placed. The method of claim 7.

9. The evaporation step involves heating the object to be soldered in a vacuum. The method according to claim 7 or claim 8.

10. The evaporation process creates gaps between the solder powder particles, The reducing step includes introducing a reducing gas into the gap while the solder powder and the object to be soldered are in a vacuum. The method according to any one of claims 7 to 9.

11. The solder melting step involves heating the solder powder and the object to be soldered in a vacuum to melt the solder powder and obtain an integrated solder joint: a vacuum breaking step after the solder melting step, in which the vacuum is broken to compress and reduce or eliminate the internal voids of the solder joint; a cooling step of cooling the object to be soldered after the vacuum breaking step; The method according to any one of claims 7 to 10.

12. The reducing gas is formic acid gas. The method according to any one of claims 7 to 11.

13. a coating step of coating the residue-free flux according to claim 1 or 2 onto a BGA package substrate as a temporary fixing agent; a temporary fixing step of temporarily fixing solder balls to the applied residue-free flux; an evaporation step of heating the BGA package substrate coated with the residue-free flux within a range that does not melt the solder balls, thereby evaporating the second solvent; a reduction step of reducing the solder balls and the BGA package substrate with a reducing gas in parallel with or after the evaporation step; a forming step of heating the solder balls and the BGA package substrate after the reducing step to bond the solder balls to the BGA package substrate and form solder bumps; The first solvent and the fatty acid amide evaporate together with the second solvent in the evaporation step, or evaporate as a result of heating in the formation step. A manufacturing method for a BGA package.

14. an application step of applying the solder paste according to any one of claims 3 to 5 to an object to be soldered; a bump placement step of placing solder bumps of a BGA package on the applied solder paste; an evaporation step of heating the object to be soldered onto which the solder paste has been applied within a range in which the solder powder and the solder bumps do not melt, thereby evaporating the second solvent; a reduction step of reducing the solder powder, the object to be soldered, and the solder bumps with a reducing gas in parallel with or after the evaporation step; a solder melting step of heating the solder powder, the object to be soldered, and the solder bumps after the reducing step to melt the solder powder and the solder bumps; The first solvent and the fatty acid amide evaporate together with the second solvent in the evaporation step, or evaporate due to heating in the solder melting step. Manufacturing method for soldered products.

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